Spark plug



Aug. 18, 1931. w. o. MICHELSEN SPARK PLUG Filed April 3, 29

. 2 Sheets-Sheet l 147 TOR/Y5K:

Patented Aug. 18, 1931 WILLIAM OTTO IIGHELSEN, OF WOOD'HAVEN, YORK SPARKPLUG Application filed April 3, 1929. semi so.

This invention relates to new and useiul improvements in spark plugswhich are especially; adapted for' use in connection with automobileinternal Combustion engines. j It is aknown fact, that whenstarting anin- "ternal combustion engine while it is cold, by means of an electricmotor that is" supplied with electric currentfrom a battery, whichsimultaneously'is furnishing current for the ignition system of mnt thatis generally embodied in the power plant ofan automobile, that thisbattery is often overloaded by the heavy o the starting motorimposesupon it This heavy discharge is. still further increased in cold weatherwhen the oil in the engine is con E'gea'led and resists the efforts ofthe starting motor to a greater extent, eflecting a considerablelowering ofthe voltage. available for ignition of the "engine.Frequentlythe gap formed between the spark plug electrodes,too wide forthe purpose of starting the engine, causes failure to produce a sparkuntil after the'engine has been turned over? a number of times and theresistance of the crank case oil has thereby been reduced. This isarticularlytrue when the battery is not ully charged. a I

\ Oneoftheprincipal objects of my inven-, tionis to provide a spark.plug which will vary automatically the size of the spark gap in ac-'cordance with thetemperature ofthe engine.- Another object of theinvention lies in the provision of a spark plug havingtwoelectrodes'normally forming therebetween two spark gapsofrelativelysmaller and larger sizes, one o the electrodes being movableunder the application of increased heat to increase the smaller gap to asize at least equal to-the size of the larger gap without varyingthesize of said larger gap. p A further object of my invention is toprovide the insulator of the spark plug with a re-, W cess whichsurrounds the central electrode in such a manner as tolreduce to aminimum the danger of shortoircuitingbetween the central electrode, vthe,insulatorvandthe conductor shell to'which the groundeleetrode is fixed.A. still furtherfob ect of the invention is to provide means associatedwith the recess will more fully appear,

said engine, an arrange- I .xa spark lug embod in discharge that p y gthereof, and

which surrounds the central electrode for reducing to a minimum theaccumulation of carbon within said recess.

With these and other objects in view which the nature of the in- Ivention' will be more clearly understood by following the description,the appended claims, and the several views illustrated in theaccompanying drawings.

p In the drawings:

Figure 1 is a longitudinal sectional View of the preferred form' of myinvention,

Figure 2 is a complete view of the inner end thereof, V I I Figure 3 isa view similar to Figure 1 but showing another form of my invention,

Figure 4; is a complete view of the inner end thereof,

Figure. 5 is a view similar to Figure 1 but showing another form of myinvention,

Figure 6 is a complete view of the inner end thereof,

Figure 7 is a view partly in side and partly in section of my invention,s

Figure 8 is a complete View of the inner end elevation Figure 9 is acomplete end View of another form of my invention showing the structuresof Figures 5 and 7 combined.

Like reference numerals designate corresponding parts throughout theseveral figures of the drawings.

Referring to the drawings and particu- 8 larly to Figures 1 and 2, Ihave shown a spark plug which comprises a conductor shell A, aninsulator B mounted therein and retained in position by a gland nut G,the inner end 5 of the insulator being disposed within the shell and theouter end 6 of the insulator. projecting for a considerable distancebeyond the gland nut. The outer end 6 of the insulator is. provided withan axial opening which communicates with a longitudinally and axiallylocated recess 8, the latter extending from the inner end 5 to a pointbeyond the gland nut C where it forms a resultant end wall or shoulder9. 7

Attached to the inner end of the shell is showing another form 75 i aground electrode 10 having a longitudinally extending attaching shank 11and an inward lv radially extending arm 12.

Axially disposed within the recess 8 of the insulator B is a centralelectrode 13 comprising a rod 14 of copper or of other suitable metal,which will expand and contract under temperature changes, and a reducedextension which is preterably a separate parttitted into an axial borein the inner end of the rod. The rod 14 is substantially coextensivewith the insulator l3 and the outer end of the rod is removably fittedwithin the axial opening 7 thereof. it flange 16 on the rod 14 locatedwithin the recess 8 and cooperates with the end wall or shoulder 9 toprevent outward movement of the rod relative to the insulator. The outerend of the rod 14 projects beyond the insulator B and is threaded as at17. A washer 18 surrounds the threaded outer end of the rod 14 and bearsst the end of the insulator, and clamping nuts 19 have threadedengagement with the threaded portions 1'? of the rod for clamping theflange 16 tightly against the shoulder 9. Thus the central electrode 13may be readily positioned in the insulator B or removed therefrom. Aterminal nut 20 is also e ged with the threaded portion 17 of the rod Q:for cooperation with the clamping nuts 19 to secure a lead wire to thecentral electrode. If desired. suitable packing may be interposedbetween the shoulder 9 and the tlange 16. Extension 15 includes a shank21 and an inwardly and radially extending arm The sha s 11 and 21 of thetwo electrodes together with the arms 12 and 22 thereof, are alldisposed in a common plane and the arms 12 and 22 are arranged inslightly overlapping relation so as to form therebetween a variablespark gap X. The terminal end of the arm 12 is spaced from the shank 91to term a substantially constant spark gap Y. By substantially constantspark gap I mean a gap whose width varies only to a neglibible extentincident to the expansion of the arm 12 ot' the electrode 10. Thiselectrode is formed of a metal having a low coellicient of expansionsuch as that possessed by electrodes used in ordinary spark plugs inwhich the single spark gap is necessarily substantially constant. Thevariation in the 'idth of the gap Y is negligible, whereas there anappreciable variation in the width of the gap X at ditlerenttemperatures. The substantially constant spark gap Y is preferably oi.standard width. whereas the variable spark gap X is normallyconsiderably narrower than the substantially constant gap Y. Therefore.I have provided a relatively narrow gap X and a relatively wide gap Y.Thus when the engine is first started, the spark will jump the gap Xfrom the arm 22 to the arm 12 and as the engine gets warmeig the centralelectrode 13 will expand longia gr tudinally and consequently the sparkgap X will be automatically increased until said gap equals thesubstantially constant gap Y at which time the spark will jump acrosseither or both gaps. If the central electrode is further elongated byreason of its inherent expansion the spark will then only jump acrossthesubstantially constant gap Y.

The diameter of the recess 8 in the insulator is considerably greaterthan the diameter of the central electrode 13 and consequently an airspace is formed around that portion of the electrode which is locatedwithin the recess. Thus the rod 14 ot' the central electrode will becomecompletely surrounded by high compressed gases at the time of eachspark, and these compressed gases serve as an additional insulationbetween the rod and gland nut. This insulation is especiallyadvantageous should the insulator B be formed of porcelain or otherporous material. u reason of the recess extending beyond the gland nutG, I have reduced to a minimum the possibility of shortcircuitingbetween the central electrode and the gland nut.

It is to be tance between the wall of the recess 8 and the rod 14 withinthe recess is greater than the distance of either spark gap or Y. Thisis especially valuable in preventing shortcircuiting, as above noted,for the reason that porcelain insulators very soon absorbs carbon. Themicroscopic cracks in the glaze become filled with carbon whichpenetrates the main body of the porcelain and soon causes it to becomeuseless as an insulator. It is desirable, therefore, to prevent carbonfrom accumulating in the insulator recess 8 as it would tend to lessenthe space between the rod 14 and the wall of the recess, and wouldeventually bridge said compression of the engine, and also nullifyingthe insulating property of the insulator. Furthermore the recess 8should be kept clear of carbon to permit the heat of the exploding gasesto reach the rod 14 and for this reason I have provided a check valvewhich will now be explained.

The central electrode 13 is guided during its period of expansion andcontraction by a centering washer 23 which is preferably formed ofporcelain or other insulating material. This washer 23 is secured to theelectrode 13 by being mounted on the reduced portion 15 and beingclamped between a flange 24 fixed to the shank has slidable engagementwith the recess 8. This washer 23 is provided with a series of openings25 which afford communication between the cylinder of the engine and therecess 8 of the spark plug. A check valve 26 is located Within therecess 8 and is slidwall of the noted that the minimum disspace,shutting out'the ably mountedon the rod-14 for cooperation withtheopenings 25. A coil spring 27 is disposed around the rod 14 andone endbears against the valve .26 and the other end bears against a flange 28functionsto yieldably retain the valve in its closed position;

- When'the engine is the usual starter or by mixture is drawn into thecylinders.-

being started, either by a crank, a charge of gas This I charge is,compressed by the upward stroke of the pistons: and this compressed.charge forces the valve 26 to be unseated and some of the compressedmixture is thereby directed into recess8 of the insulator. At this timethe ignition spark occurs and causes the ex- 'plosion in the combustionchamber, the exploded gases passing into the recess 8 through theopen-ings 25. Immediately after the explosion the check valve will closeautomatically by means of the spring 27 and by reason of thepressurebeing equal on both sides of the valve. Theclosure' of the valvewill there by trap the burned gasesat near the explosion compressionwithin the recess 8. The piston during the exhaust stroke thereof willforce out-"of the cylinder all burned gases which have not been trappedwithin the recess 8. When the cycle ofoperation is repeated, fresh gaseswill not enter the recess 8, except for a negligible-quantity, becauseof the presence of the burned gases already locatedwithin the recess.Consequently the actual flame of the explosion, which will occur onlywhere there areignitable gases, and which is the agent that causescarbon to be deposited, will not reach into the recess 8 after the firstfew combustion operations have taken place. Suflicient heatat the timeof the explosions will enter through openings 25, due to the compressionbeing stronger than the resist ance of the spring 27, and consequentlythe rod 14 willbecome heated as the engine func- I tions. r Referring toFigures 3 and 4which show another form of my invention, I have discloseda conductor shell A, an insulator D arrangedtherein'and held againstmovement by a gland nut O, The insulator D is form ed with a'recess29'similar to the recess 8; A groundelectrode 10 is fixed to the-shell Aand a central electrode SO'isdi'sposed within .the.

I recess 29andisprovided with a reduced extension for cooperation withthe. ground I electrode 10. The central electrode 30 has its outer'endmounted in an axial opening 31 formed in the insulator and is heldagainst longitudinal movement relative to the insula tor by an expandedsocket B2'formed on the end of a projecting rod 33; The socket 32 isdisposed within alrecess 34 formed in the outer end ofthe insulator anda packing: 35 of cement or other suitable material is disposed withinthe "recess around the socket. A cap 36 isp'laced over the outer end ofthe formed on said rod and insulator D and a packing 37 is placedbetween them. The rod 33 is threaded for engagement with a clampingnut38 and also threaded on the rod and cooperating with the clamping'nut 38isa clamping nut 39 for securing-a lead wire therebetween. The inner endof therod 30 is guided in its longi tudinal movements during expansionand contraction by reason of a plurality of guide or centering arms 40which are preferably integral with the insulator body. These arms arerelatively narrowso as to form resultant spaces 41 therebetween forpermitting the heat to pass into rectly affect the central electrode.

By reference to Figures 5 and 6, the form therein shown includes aconductor shell A, an insulator D mounted therein and a gland nut C. Theinsulator D is formed with a recess 42 similar to the recessesS and 29.Fixed to the inner end of the conductor shell A is a ground electrode 43which includes an attaching shank 44, an inwardly and radially extendingarm 45, and a terminal arm 46 which extends at right angles to thelongitudinal axis of the arm 45. Located within the recess 42 is acentral electrode 47 which includes a substantially non-expansible rod48 and an appreciably expansible rod 49, the rods being spot welded orotherwise rigidly connected as at 59, 50. The outer end of the centralelectrodeis connected to a socket 32 in the same manner as described inconnection with the form shown in Figure 3. The inner end of the rod 48extends beyond the terminal arm 46. Opposite guides 51, 51, preferablyformed integral with the insulator D, extend inwardly from the inner endofthe recess 42 and function to guide the central electrode during itsexpansion and contraction, and also serving to maintainthe movement ofthe electrode in a fixed plane. Thus when the engineis operated and theexpansible rod 49 becomes heated, said rod will elongate and cause theouter end of the rod 48 to be moved downwardly away from the arm andthereby vary the spark gap X, and at the same time maintainsubstantially constant the spark gap Y between the end of the rod 48 andthe terminal arm. 46.

In the form illustratedlin Figures 7 and 8, I have provided a conductorshell A, an insulator E mounted therein and held against movement by agland nut C. The insulator E is formed with a longitudinal opening I 52which extends substantially throughout the length of the insulator andmounted in-this opening is a central electrode 53 having at its innerend a reduced extension 54 which inv cludes an attaching shank 55 and anarm 56 the recess 29 and thereby di.

which extends V inwardly and radially therefrom. The inner end of theconductor shell A is formed withan interior seat 57 and mounted in thisseat is a coiled electrode 58 having one end 59 fixed within an openingformed in secured to the outer the arm 61 parallelism the shell. Theouter end of the coil termi nates in a longitudinally extending shank 60which in turn is bent to form an arm 61 and a terminal arm 62 arrangedat right angles to and extending inwardly and in with the arm 56. Thesearms 56 and 62 are normally spaced apart a distance to provide avariable spark gap X and the minimum distance between these arms ismaintained by means of a stop 63 which is fixed to the shell A forcooperation with the extension 60. The space between the terminal end ofthe arm 56 and the arm 61 forms a substantially constant gap Y. Thuswhen the engine is operated, the rod 58 which is formed of expansiblemetal will expand under the action of heat and cause the arm 62 to moveaway from the arm 56 thereby increasing the gap X while maintaining thegap Y substantially constant.

In the form illustrated in Figure 9, I have combined the structuresshown in Figures 5 and 7 whereby both the central electrode 47 and theground electrode 44 will be moved simultaneously in opposite directionsto quickly vary the variable gap X but, however, without appreciablyvarying the constant gap Y.

I claim:

1. In a spark plug, a conducting portion and an insulating portion, andtwo electrodes respectively connected to said portions and normallyforming two constantly open spark gaps of relatively smaller and largersizes between said two electrodes, one of said electrodes being movablerelatively to the other to increase the size of the smaller gap withoutvarying the size of the larger gap.

2. In a spark plug, the combination with a conductor shell, of aninsulator mounted therein and formed with a longitudinally and axiallylocated recess extending from the inner end toward the outer endthereof, an electrode located within and extending longitudinally ofsaid recess and having one end' end of the insulator and having itsother end projecting beyond the inner open end of the insulator, saidelectrode including a straight metal rod having a relatively highcoefficient of expansion and movable lengthwise under the influence ofheat, guiding means for the inner end of the electrode for maintainingsaid inner end in spaced relation to the wall of the recess and forpermitting longitudinal movement of the electrode, and an electrodesecured to the shell for cooperation with the first mentioned electrodeto form a spark gap therebetween.

3. In a spark plug, the combination with a conductor shell, of aninsulator mounted therein and formed with a longitudinally and axiallylocated recess extending from the inner end toward the outer endthereof, an electrode located within and extending longitudinally ofsaid recess and having one end removably secured to the outer end of theinsulator and having its other end projecting beyond the inner open endof the insulator, said electrode including a straight metal rod having arelatively high co-eificient of expansion and movable lengthwise underthe influence of heat, guiding means for the inner end of the electrodefor maintaining said inner end in spaced relation to the wall of therecess and for permitting longitudinal movement of the electrode, saidguiding means being mounted on the inner end of the rod for cooperationwith the wall of the recess, and an electrode secured to the shell forcooperation with the first mentioned electrode to form a spark gaptherebetween.

4. In a spark plug, a conducting portion and an insulating portion, andtwo electrodes respectively connected to said portions and normallyforming two constantly open spark gaps of relatively smaller and largersizes between said two electrodes, one of said two electrodes includinga metal rod having a relatively high co-eiiicient of expansion andmovable in a direction under the influence of heat to increase the sizeof the smaller gap without varying the size of the larger gap.

5. In a spark plug, a conducting portion and an insulating portion, aground elect-rode connected to the conducting portion, and a centralelectrode connected to the insulated portion and movable longitudinallyin response to temperature changes, said electrodes each including ashank and an inwardly extending and substantially radially disposedterminal arm, the arms being disposed in overlapping relation to formtherebetween a variable spark gap, the terminal end of the arm of theground electrode being spaced from the shank of the central electrode toform therebetween a substantially constant spark gap.

6. In a spark plug, the combination with a conductor shell, of aninsulator mounted therein and formed with a longitudinally and axiallylocated recess extending from the inner end toward the outer endthereof, an electrode located within and extending longitudinally of,said recess and having one end secured to the outer end of the insulatorand having its other end projecting beyond the inner open end of theinsulator, said recess terminating at a point beyond the outer end ofthe shell and having a diameter greater than the diameter of theelectrode to form an annular space between the wall of the recess andthe electrode, an electrode secured to the shell for cooperation withthe first mentioned electrode to form a spark gap therebetween, and acheck-valve located within the recess at the inner end of the insulatorand opening toward the closed end of the recess.

7 In a spark plug, the combination with a conductor shell, of aninsulator mounted therein and formed with a longitudinally and axiallylocated recess extending from the inneri end toward the outer endthereof, an electrode movable. electrode for, maintainingisaidinlner,end in spaced relation to; the wall ofathe located within and extendinglongitudinally of said recess and having one end secured to the outerend of the insulator and having its other end projecting beyond theinner open end of the insulator, said recess terminating at a pointbeyond the outer end ofwtherein and formed. with a longitudinally theshell and having a diameter greater than the diameter of the electrodeto form an annu-- lar space between the wall of the recess and @fixedelectrode secured to said shell, a movthe electrode, an electrodesecured to the shell for cooperation with the first mentioned elec-,

trode to form a spark gap therebetween, a perforated washer attached tothe central electrode at the inner end of the insulator and havingslidable contact with the wall of the recess, a valve slidably mountedon the cen tral electrode for cooperation with the perforations of thewasher, and a spring for yieldably retaining the valve against thewasher. I

8. In a spark plug, the combination with a conductor shell, of aninsulator mounted therein and formed with a longitudinally and axiallylocated recess extending from the inner end toward the outer endthereof, an electrode located within and extending longitudinally ofsaid recess and having one end secured to the outer end of the insulatorand havingits other end projecting beyond the inner open end oftheinsulator, said recess terminating beyond the outer end of the shell andhaving a diameter greater than the di ameter of the electrode to form anannular space between the wall of the recess and the electrode, anelectrode secured to the shell for cooperation with the first mentionedelectrode to form a spark gap therebetween, and a check-valve locatedwithin the recess at the inner end of the insulator and opening towardthe closed end of the recess, the outer end of the centralelectrodebeing removably connect,

ed to the insulator to permit removal of the electrode together with thecheck-valve from the insulator.

9. In a spark plug, the combination with a conductor shell, of aninsulator mounted therein and formed with a longitudinally and axiallylocated recess extending from the inner end toward the outer endthereof, a fixed electrode securedto said shell, a mow able electrodelocated within and extending longitudinally of'the recess in saidinsulator and having one end secured to the outer end of the insulatorand having its other end projectingbeyond the inner open end thereof,the projecting end of said movable electrode cooperating with said fixedelectrode to form two constantly open spark gaps of relatively smallerand larger sizes, said movable electrode including a straight metal rodhaving a relatively high co-eflicient of expansion and movablelengthwise under the influence recess andfor permittinglongitudinalrmovement, of'the electrode.

1 r10; Infa spark plug, thercombinationwith I a rconduotor shell; of 1an insulator mounted and, axially located-recess extending from. the1111161. end toward the outer endthereof, a

able electrode locatedwithin and extending longitudinallyof the recess;in saidinsulator and having one end secured totheiouterend of. the.insulator and 1 having its other end projecting beyond the inner openend thereof, the projecting end of said movable electrode cooperatingwith said fixed electrode to form two constantly open spark gaps ofrelatively smaller and larger sizes, said movable electrode including astraight metal rod having a relatively high co-efficient of ex pansionand movable lengthwise under the influence of heat to increase the sizeof the smaller gap without varying the size of the larger gap, andguiding means mounted on the inner end of the rod for cooperation withthe wall of the recessffor maintaining said inner end in spaced relationto the wall of the recess and for permitting longitudinal movement ofthe movable electrode.

11. In a spark plug, the combination with a conductor shell, of aninsulator mountedtherein and formed with a longitudinally and axiallylocated recess extending from the inner end toward the outer endthereof, an

electrode located within and extending 1011- ;having its other endprojecting beyond the inner open end of the insulator, the recess insaid insulator terminating at a point beyond the outer end of the shelland having a diameter greater than the diameter of the electrode to forman annular space between the wall of the recess and the electrode, anelectrode secured to the shell for cooperation with the first mentionedelectrode to form a spark gap therebetween, and centering meanscooperating with said first mentioned electrode and with said insulatorto maintain said gap substantially constant.

12. In a spark plug, he combination with a conductor shell of aninsulator mounted therein and formed with a longitudinally and axiallylocated recess extending from the inner end towardthe outer end thereof,an electrode located within and extending lon-. gitudinally of, saidrecess and having one end secured to the outer end of the insulator andhaving its other end projecting beyond the inner end of the insulator,said recess term nating at a point beyond the outer end of the shell andhaving a diameter greater than the diameter of the electrode to form anannular space between the Wall of the recess and the electrode, saidelectrode includ ing a straight metal rod having a relatively highco-etficient of expansion and movable lengthwise under the influence ofheat, guiding means for the inner end of the electrode for maintainingsaid inner end in spaced relation to the wall of the recess and forpermitting longitudinal movement of the electrode, and an electrodesecured to the shell for cooperation with the first mentioned electrodeto form a spark gap therebetween.

In testimony whereof, I have hereunto subscribed my name.

WILLIAM OTTO MICHELSEN.

